by Carl Strang
This is the third installment describing my 2008 vacation to look at the route followed by the Lake Michigan lobe of the latest (“Wisconsin”) glacier. I followed the highway northeast to Timmins, Ontario, and camped a couple nights at the nearby Kettle Lakes Provincial Park. This is an area where the bedrock is covered by glacial drift and outwash, as is the case in DuPage County. As I explored the park’s trails I was struck by how familiar the outwash looked. The colors and proportions of little stones seemed very similar to ours, except for the absence of the Devonian shale and the Niagara dolomite. Those would not be expected, because they are from the bottom of Lake Michigan and from its rim, well downstream from Ontario on the glacier’s route.
Outwash at Kettle Lakes
The story was different at Nagagamisis Provincial Park, which I reached after driving far enough northwest that I was northeast of Lake Superior. The drift stones at Nagagamisis had different colors in different proportions and did not look familiar. This is intuitive rather than a quantitative measurement, but I feel pretty confident about it. There were plenty of basalts, but a higher proportion of white granites, and few red granites and gneisses. The surprise was that there was a presence of Paleozoic sedimentary pieces, including fossils. When I examined the maps I found that the glacier indeed had passed over an area of Paleozoic bedrock that lies between Hudson Bay and Nagagamisis.
Outwash at Nagagamisis
Closeup of horn coral fossil
A couple days later I camped on the shore of Lake Superior at the Agawa campground of Superior Provincial Park. The stones on the beach there were dominated by reddish granites and black basalts or diabases. There were pale quartz pieces, but little or no sedimentary rock. The high proportion of red granites, a significant percentage of which were mixed with greenstone minerals, was surprisingly unlike what we see in DuPage County. I would have thought this spot was in the path of the Lake Michigan lobe, but that appears not to be the case.
Agawa beach stones
Agawa beach closeup
My next examination of drift was at Whitefish Point, near the tip of the Upper Peninsula of Michigan on the Lake Superior side. Here the rock mix was, to the eye, familiar and like that of NE Illinois. This spot seems unavoidably in the path of the Lake Michigan lobe.
Whitefish Point beach stones
A final stop, at Illinois Beach State Park, was similar except that the local Paleozoic stones were back in the mix.
Illinois Beach State Park stones
This all was satisfying, though my tentative conclusions don’t withstand close scrutiny. A quantitative and perhaps chemical examination of the rocks would be necessary to nail it down. However, my observations are consistent with mapped glacial scratches on bedrock. It appears to me that the Lake Michigan lobe passed through or near Timmins, on the one (S or SE) side, and Whitefish Point and Door County on the other (N or NW). One test of this idea I intend to make in a future inquiry will be to search for drift on the U.P. west of Whitefish Point. I would expect to find, somewhere, a match to Agawa Bay.
There will be one final entry in this series, focusing on the biology of the part of Canada I explored on this trip.
Tree Tracking « Nature Inquiries said,
March 26, 2009 at 3:07 am
[…] are other forms of tracking. I have in fact provided examples in posts on the mastodon dig and on glacial geology, as well as various posts on archeology. When I teach tree tracking to kids I always begin by […]